1. Field of the invention
The present invention relates to an automatic document feeder, and more particularly to an automatic document feeder which feeds a document onto a platen glass of a copying machine automatically and ejects it therefrom.
2. Description of Related Art
Recently, in a field of electrophotographic copying machines, various automatic document feeders (ADF) are provided to save a trouble of changing documents and develop the copy processing ability. An ADF feeds a document one by one from a tray and sets it in a specified position on a platen glass and ejects it therefrom after the document is scanned.
The ADF is fitted by hinges in a rear side of the copying apparatus and is capable of pivoting on the hinges so as to be lifted up when an operator sets a document on the platen glass manually. A conveyer belt of the ADF has to be in contact with the platen glass evenly.
However, because of errors in production of the parts and in assembly of the machine, a problem occurs in setting the conveyer belt on the platen glass. For example, because the level difference between the surface on which the hinges are fixed and the surface of the platen glass varies from machine to machine or because the surface on which the hinges are fixed and the surface of the platen glass may not be exactly parallel to each other, the conveyer belt can not be in contact with the platen glass entirely with an even pressure.
Conventionally, in order to solve the problem, when the machine is set up, spacers are provided between the surface of the machine body and the hinges so that the level of the hinges can be adjusted to the level of the surface of the platen glass. However, this adjustment must be carried out differently and properly for each machine, and this is troublesome.
In order to save the adjustment, as shown in FIG. 5, a whole ADF 10 including a document conveying section is fitted to a supporting flame 24 through regulating plates 11 and 12 and is capable of pivoting on hinges 20. Thereby, the difference in angle between the platen glass and the ADF 10 can be decreased. However, in the ADF 10, while the ADF 10 is closing, when the regulating plate 11 which is provided in the rear side of the ADF 10 comes into contact with the platen glass 31, the weight of the whole ADF 10 is applied on the contact portion of the platen glass 31 and at the same time, the load on the hinge 20 is decreased rapidly. This means that a power which is needed to close the ADF 10 (pressing power) further from the state of FIG. 5 becomes larger. This causes an inconvenience in the operation, and a magnet 15 which is used for keeping the ADF 10 in contact with the apparatus body 30 requires a larger magnetic power. A dashed line shown in a graph of FIG. 3 shows a change of the pressing power which is needed to close the ADF 10. This shows that the pressing power becomes larger by .alpha. rapidly when the opening angle of the ADF 10 goes over a free stop area.